Transcriptional Gene Silencing Mediated by a Plastid Inner Envelope Phosphoenolpyruvate/Phosphate Translocator CUE1 in Arabidopsis

Mutations in REPRESSOR OF SILENCING1 (ROS1) lead to the transcriptional gene silencing (TGS) of Pro(RD29A):LUC (LUCIFERASE) and Pro(35S):NPTII (Neomycin Phosphotransferase II) reporter genes. We performed a genetic screen to find suppressors of ros1 that identified two mutant alleles in the Arabidopsis (Arabidopsis thaliana) CHLOROPHYLL A/B BINDING PROTEIN UNDEREXPRESSED1 (CUE1) gene, which encodes a plastid inner envelope phosphoenolpyruvate/phosphate translocator. The cue1 mutations released the TGS of Pro(35)S:NPTII and the transcriptionally silent endogenous locus TRANSCRIPTIONAL SILENCING INFORMATION in a manner that was independent of DNA methylation but dependent on chromatin modification. The cue1 mutations did not affect the TGS of Pro(RD29A):LUC in ros1, which was dependent on RNA-directed DNA methylation. It is possible that signals from chloroplasts help to regulate the epigenetic status of a subset of genomic loci in the nucleus.